Filtering air entering a spray-dryer through actuated charcoal in the preparation of spray dried whole milk

ABSTRACT

An improvement in the process producing spray-dried while milk wherein the air entering the spray-dryer is filtered through activated charcoal to remove the ozone therefrom. The flavor quality of the resulting product is preserved and prevented from deteriorating, and with ozone-free air the flavor quality of the spray-dried product is the same as the milk concentrate from which it is made.

United States Patent Inventors Appl. No.

Floyd E. Kurtz Bethesda, Md.;

Arjen Tamsrna; Michael J. Pallansch, Arlington, Va.

Jan. 29, 1970 Oct. 26, 1971 The United States of America as representedby the Secretary of Agriculture FILTERING AIR ENTERING A SPRAY-DRYERTHROUGH ACTUATED CHARCOAL IN THE PREPARATION OF SPRAY DRIED WHOLE MILK 4Claims, No Drawings Int. Cl A23c l/04 Field of Search 99/203, 56

References Cited OTHER REFERENCES Kurtz, Tarnsma, and Pallansch Effectof Filtering Ozone- Polluted Dryer Air Through Activated Charcoal on theFlavor of Foam Spray-Dried Whole Milk in Journal of Dairy Science, 52,425- 427, 1969.

Hall and Hedrick, Drying of Milk and Milk Products, Avi Publishing Co.,Inc. (1966) pp. 59- 93.

Primary Examiner-S. Leon Bashore Assistant Examiner-Richard H. TushinAttorneys-R. Hoffman and W. Bier ABSTRACT: An improvement in the processproducing spray-dried while milk wherein the air entering the spraydryeris filtered through activated charcoal to remove the ozone therefrom.The flavor quality of the resulting product is preserved and preventedfrom deteriorating, and with ozonefree air the flavor quality of thespray-dried product is the same as the milk concentrate from which it ismade.

FILTERING AIR ENTERING A SPRAY-DRYER THROUGH ACTUATED CHARCOAL IN THEPREPARATION OF SPRAY DRIED WHOLE MILK A nonexclusive, irrevocable,royalty-free license in the invention herein described, throughout theworld for all purposes of the United States Government, with the powerto grant sublicenses for such purposes is hereby granted to theGovernment of the United States of America.

The invention relates to a method of improving the flavor of spray-drieddairy products and more particularly to a method of eliminating from thespray-drying process factors responsible for loss of flavor quality.

Prior to the present invention, the standard practice in producingspray-dried dairy products was to filter the air entering the dryerthrough cellulose or similar type filters to remove dust and otherforeign particles. However, regardless of the filter used, the flavorquality of the products was not consistent. This inability toconsistently obtain a product having good flavor quality represented aserious drawback to commercial production of spray-dried dairy products.

An object of this invention is to improve the flavor of spraydried dairyproducts.

Another object of this invention is to eliminate from the spray-dryingprocess substances responsible for loss of flavor quality.

A further object is to provide a process whereby variations in productflavor and quality are eliminated and high quality spray-dried dairyproducts having excellent flavor characteristics are producedconsistently.

We have discovered that the causative agent for the offflavors and theresultant inconsistencies in flavor quality of spray-dried dairyproducts is an air pollutant, ozone. We have also discovered how toremove the ozone and eliminate its effects and consequently how toconsistently produce a high quality spray-dried dairy product.

According to this invention the flavor of a milk concentrate ispreserved in the spray-dried whole milk into which it is processed byreplacing the standard cellulose type dust filters with activatedcharcoal filters. In addition to removing dust and other foreignparticles from the air entering the dryer, the charcoal filters reducethe ozone level of the entering air to zero. When the air is ozone-free,a high quality product with excellent flavor characteristics is producedconsistently.

Experiments were conducted to prove the effectiveness of this inventionin attaining the previously stated objectives. Foam spray-dried milk wasprepared from low-heat whole milk using nitrogen for foaming asdescribed in J. Dairy Sci., 45, 27-31, 1962.

The powders were made from milk collected from a herd over a 3-dayperiod before drying. The milk was standardized to 3.3 percent fat,heated for IS seconds at 77 C., homogenized, and concentrated to 50percent solids in a falling film evaporator of 100 gallons-per-hourcapacity. The concentrate was fed at a rate of about 10 lbs. per minuteto a modified spray dryer equipped with a pressure nozzle. Themodification consisted of providing means for injecting nitrogen gasunder pressure into the feed line between pump and nozzle. This wasaccomplished by use of a stainless steel, modified T joint in the feedline. The flow of nitrogen (57 liters per minute) was determined by useof a high-pressure flow meter and manually controlled by a needle valvein the line. Air entering the dryer at a constant rate of approximately7,000 cu. ft. per minute and at a temperature of about 132 C. wasemployed in making the spray-dried powders. The temperature of thepowder emerging from the spray-dryer was about 60 C. and was cooled withliquid nitrogen to about room temperature before exposure to plant airoutside the dryer. The hot dried powder was fed by a star valve into ascrew conveyor which carried the powder to a collecting receptacle. Thewhole collecting system had previously been purged of air by nitrogenflushing. Liquefied nitrogen was metered at a rate of 500 grams perminute into the conveyor to cool the powder to 26.7 C. as described inJ. Dairy Sci., 50, 1873-1877, 1967.

The experiments to obtain the data shown in tables 1 and 2 wereconducted as follows: Using standard cellulose dust filters, milk powderfrom 11 kg. of milk concentrate was discarded so that the dryer would beclear of any preceding powder. Then powder sample A, without screeningand with a I minimum of exposure to air, was collected directly in acontainer which was immediately capped until the powder wasreconstituted for tasting. The cellulose filters were replaced withactivated charcoal filters, powder from 33 kg. of concentrate wasdiscarded as above, powder from 1 1 kg. of concentrate was collected ina milk can and then powder sample 8-] without screening and with aminimum of exposure to air, was collected directly in a container whichwas immediately capped. The powder collected in the milk can was heldfor 20-25 minutes in the capped can, screened in the surrounding ozonepolluted air and then stored in a capped container until reconstituted.This was sample 8-2. The charcoal filters were then replaced withcellulose filters and powder sample C collected directly in a jar afterdiscarding powder from 33 kg. of milk concentrate.

Each of the activated charcoal filters used in the experimen tal workcontained 45 lbs. of charcoal, had a rated capacity for the passage ofair of 1,000 cu. ft. per minute, and was approximately 2 ft. high, 2 ft.wide and 8% inches deep. Since each filter was folded a number of timesand in such a manner that' it was like a layered series of filters witheach layer containing part of the total 45 lbs. of charcoal, the depthof 8% inches was not solid charcoal. in order to cover the air inletopening in the dryer used in the experimental work described in thisapplication, nine of the activated charcoal filters were used.

Filter changes took l0-l5 minutes and during this time water instead ofthe concentrate was fed into the dryer. Measurements of ozone in theincoming dryer air were made as previously described (.1. Dairy Sci.,52, 158, 1969) with the inclusion of a chromium trioxide scrubber forremoving sulfur dioxide. Milks were reconstituted from the powdersamples and refrigerated overnight. The flavor of these milks was thenevaluated by a trained taste panel using a 10-point scoring range of31-40 (J. Dairy Sci., 49, 628, i966). All powders were tasted induplicate. Samples of the original milk concentrate were taken at thebeginning and at the end of each experiment, and their scores, whichwere in very close agreement, averaged for the flavor score shown intables I and 2.

As shown in table I a marked improvement in flavor quality is obtainedwhen the incoming ozone-polluted air is filtered through activatedcharcoal. Using cellulose filters (powders A and C) the ozone level inthe dryer varied from 4 to 17 ppb, and from 0.6 to 4.0 flavor pointswere lost in the drying process. In contrast, using charcoal filters theozone levels were reduced to zero and the flavor scores varied from 0.2higher to 0.7 lower than the concentrates.

When the powder was cooled before exposure to polluted air, subsequentexposure incident to screening and packaging did not have an adverseeffect on the flavor score as shown in table 2.

In order to determine whether low levels of ozone in other wise pure aircause flavor damage, two experiments involving four milk powders each asshown in table 3 were conducted. Powder D was made with the addition ofozone in the incoming dryer air between the charcoal filter and theblower. Powder E was made in the same way as D except that a lower levelof ozone was added. Powder F was made using charcoal filters but with noadded ozone. Powder G was made using standard cellulose filters with noadded ozone. As in previous experiments sufficient powder was discardedbetween each collection to clear the dryer of the preceding powder.These powders, along with milk concentrate samples collected at thebeginning and end of each experiment were evaluated as described above.in addition to showing that low levels of ozone in otherwise pure air dosubstantially damage the flavor of dried milk, table 3 also shows thatthe process of this invention is very effective in preventing flavordeterioration in spray dried whole milk. When charcoal filters are usedand no ozone added, the flavor of the dried product is essentially thesame as that of the original milk concentrate.

The process described herein for spray-dried whole milk is alsoapplicable to skim milk and to other dairy products.

TABLE l.EFFECI ON FLAVOR OF FOAM SPRAY-DRIED WHOLE MILK OF USINGACTIVATED CHARCOAL FIL- TERS TO REMOVE OZONE FROM DRYER AIR Milk powderA+C B-l B/Iilk concentrate, 1 Ozone Ozone Experiment avor level, Flavorlevel. Flavor No. score p.p.b. score 2 p.p.b. score 1 Original milkconcentrate from which powders A, C and B-1 were prepared.

9 Average of powder samples A and 0.

TABLE 2.-EFFECT OF EXPOSURE TO POLLUTED AIR ON FLAVOR OF FOAMSPRAY-DRIED WHOLE MILK MANU- FACTURED IN OZONE-FREE AIR Milk powder B-lB-2 Ozone Ozone Milk conlevel in level in centrate) charcoal pollutedExperiment flavor purified Flavor plant air Flavor N 0. score air.p.p.b, score p.p.b score Table ll-Continued 1 On'ginal milk concentratefrom which powders B-1 and B-2 were prepared.

TABLE 3.EFFECI OF OZONE IN NATURALLY AND ARTI- FICIALLY CONTAMINATEDDRYER AIR ON FLAVOR OF FOAM SPRAY-DRIED MILK Milk powders 1. In aprocess for the preparation of spray-dried dairy products whereinnitrogen gas is incorporated into a liquid dairy product concentrate athigh pressure prior to spraying into a dryer into which air at atemperature of about 132 C. enters at a constant rate of about 7,000 cu.ft. per minute, the improvement which consists of filtering saidentering air through an activated charcoal filter.

2. The process of claim 1 in which the liquid dairy product concentrateis concentrated whole milk.

3. The process of claim 1 in which the liquid dairy product concentrateis concentrated skim milk.

4. The process of claim 1 in which the activated charcoal filter reducesthe ozone level of the air entering the spraydryer to zero.

2. The process of claim 1 in which the liquid dairy product concentrateis concentrated whole milk.
 3. The process of claim 1 in which theliquid dairy product concentrate is concentrated skim milk.
 4. Theprocess of claim 1 in which the activated charcoal filter reduces theozone level of the air entering the spray-dryer to zero.